Speaker 1: Welcome to brain stuff from how stuff works. Hey, I'm
Speaker 1: Christian Sager and this is brain stuff. If you're standing
Speaker 1: next to a jet during takeoff, your ear drums will
Speaker 1: probably burst. Same thing happens when you fire a twelve
Speaker 1: gage shotgun right next to your ear. When we're exposed
Speaker 1: to exceptionally loud noises, something called the stereocilia in our
Speaker 1: ears gets damaged. This causes our ears to mistakenly send
Speaker 1: signals to our auditory nerve cells. The resulting ghostly reverberations
Speaker 1: are what we call ringing ear. Many of you have
Speaker 1: probably experienced this, possibly from going to a really loud concert.
Speaker 1: The technical term for it is tenitus, and it's usually
Speaker 1: temporary unless you repeatedly damage your ears with loud noises.
Speaker 1: Then it develops into chronic tenitis, where you hear that
Speaker 1: dull ringing for the rest of your life. And that's
Speaker 1: nothing compared what really loud noise can do to you.
Speaker 1: Noise hates you, and noise can kill you. See. Sound
Speaker 1: travels in waves that enter our ear canals. These waves
Speaker 1: make our ear drums vibrate, and if they're too strong,
Speaker 1: they can snap the hair cells inside. And if these
Speaker 1: hair cells die they can never grow back. To avoid this,
Speaker 1: we use units called decibels to measure the power of sound.
Speaker 1: Anything below eighty five decibels is thought to be safe.
Speaker 1: At a hundred and fifty decibels, your ear drums burst
Speaker 1: like with the jet or the shotgun, and at two
Speaker 1: hundred decibels, your lungs will rupture and likely kill you.
Speaker 1: That's right. The threshold for death by sound is somewhere
Speaker 1: between a hundred and eighty five and two hundred decibels.
Speaker 1: What happens is the sound causes an air embolism within
Speaker 1: your lungs that can travel to your heart and kill
Speaker 1: you dead. That is, if your lungs don't burst first
Speaker 1: from the increased air pressure caused by acoustic energy. This
Speaker 1: is how happened during wars, when high energy impulse noise
Speaker 1: from explosions causes something called blast over pressure. It leaves
Speaker 1: no external injuries, but damages organs like your ears, lungs,
Speaker 1: and gastro intestinal tract. Now, acoustic weapons are actually being developed,
Speaker 1: but usually there for non lethal purposes. There's been talk
Speaker 1: of acoustic bullets to burst ear drums, incapacitate a target,
Speaker 1: or even kill them. Others claim that an infrasound generator
Speaker 1: could also be lethal, but there's been little practical evidence
Speaker 1: of such weapons so far. The closest we've seen is
Speaker 1: a long range acoustic hailing device developed by the l
Speaker 1: Rad Corporation, which can cause hearing damage from up to
Speaker 1: fifty feet or fifteen point two four meters away. Some
Speaker 1: shipping companies have started using these devices as seaborne defense
Speaker 1: against pirates. There is one device, however, that could most
Speaker 1: definitely kill you with sound. It's not a weapon, but
Speaker 1: the European Space Agency has developed a huge air horn
Speaker 1: that they used to test satellites and spacecraft, using nitrogen
Speaker 1: gas to produce sounds up to one hundred and fifty
Speaker 1: four decibels. They blast objects to make sure they can
Speaker 1: withstand the noise of a rocket launching. The e s
Speaker 1: A themselves are so concerned about how lethal this horn
Speaker 1: is they've surrounded it with half meter thick walls made
Speaker 1: of steel reinforced concrete coated with an epoxy resin to
Speaker 1: reflect noise back into its chamber. But Christian, you're asking,
Speaker 1: didn't you just say that the threshold for death is
Speaker 1: between one hundred and eighty five and two hundred decibels.
Speaker 1: It's true I did, but the E s A believe
Speaker 1: that prolonged exposure to the one hundred and fifty four
Speaker 1: decibel horn will kill you as well, probably rupturing your
Speaker 1: ear drums, vibrating your eyeballs, and destroying you from the
Speaker 1: inside out. If you're not dead, you'll probably wish you were.
Speaker 1: Check out the brainstuff channel on YouTube, and for more
Speaker 1: on this and thousands of other topics, visit how stuff
Speaker 1: works dot com.